The present invention relates generally to lens arrays, and more particularly, to lens structures for flux redistribution and for optical low pass filtering.
Lenses of all types may be found in a broad range of applications. A particular use of lenses is in illumination optics. One main purpose of lenses in illumination optics is to confine or direct light into a beam with a controlled angle, thereby directing the light into an intended area of illumination. One way to fulfill this purpose is to ensure that the beam does not have a wide angle.
For example, an office ceiling lamp that is disposed a current cubicle is designed to illuminate a work area (e.g., the desk) in the current cubicle and not an area in a cubicle three cubicles away from the current cubicle.
Another example of a lens utilized in an illumination optics application is an automobile tail light diffuser lens array. The tail light diffuser lens array is designed to confine or direct the light into a beam with a controlled angle, thereby alerting other drivers to slow down.
Prior art lens arrays include a plurality of cells that are arranged in rows and columns and that are disposed adjacent to other cells. Each cell includes a lens element. The array of lens elements generally resembles an egg carton.
One type of lens array is referred to as a convex fly""s eye lens array. FIG. 9 illustrates a cross-sectional view of a prior art convex fly-eye lens 900. It is noted that the convex fly""s eye lens array includes a plurality of convex lens elements 904.
Another type of lens array is referred to as a concave fly""s eye lens array. FIG. 10 illustrates a cross-sectional view of a prior art convex fly-eye lens 1000. It is noted that the concave fly""s eye lens array includes a plurality of concave lens elements 1004. These lenses are called xe2x80x9cfly""s-eyexe2x80x9d because the appearance of the array of lens elements resembles the eyes of a fly.
Unfortunately, these prior art lens arrays suffer from several disadvantages. It is noted that adjacent lens elements form or define a common border there between. These borders are referred to herein as cusps (e.g., cusps 910 and cusps 1010). These cusps scatter light in a forward direction in an un-controllable manner, thereby increasing the chance that the beam misses an intended area of illumination.
Furthermore, these cusps (e.g., cusps 910 and cusps 1010) act as a lossy mechanism in the backward direction. For example, there is a loss in the light flux since a portion of the light is reflected back by these cusps. In other words, when light passes through the cusps, a significant amount of light intensity is lost.
It is noted that as the number of lenses in an array increases, the number of cusps also increases, thereby aggravating the negative effects discussed previously.
The cell size is often reduced to increase the spot density to a point at which the human eye ceases to resolve the spots. The increased spot density leads to a more uniform appearance of the light. Unfortunately, as the size of the cell (e.g., the diameter) decreases, the percentage of the area occupied by the cusps with respect to the area of the cell increases, thereby resulting in more scattered light. Consequently, a higher percentage of light flux is attenuated (e.g., reflected back or scattered) as the dimensions of the cell decrease. This scattering problem caused by the cusps effectively sets a limit on the cell size and cell density.
Accordingly, it is desirable to have a lens structure whose cell dimensions may be reduced without the scattering effects and other negative effects described previously.
Based on the foregoing, there remains a need for a lens that overcomes the disadvantages set forth previously.
One aspect of the present invention is the provision of a lens structure that is devoid of cusps that exist in prior art fly-eye lenses.
According to one embodiment of the present invention, lens structures for flux redistribution and for optical low pass filtering are provided. The lens structure has a surface that includes a seamless profile, which is devoid of cusps. The surface includes a plurality convex elements and concave elements (e.g., an array of alternating elements and concave elements). The convex elements include a positive surface curvature area, and the concave elements include a negative surface curvature area.
According to another embodiment of the present invention, a lens structure can include a surface for producing a controlled amount of under-corrected spherical aberration and over-corrected spherical aberration. This surface may be employed for filtering applications, such as low pass filtering of digital images. The low pass filtering can occur prior to the light being imaged onto the imaging electronics. The low pass filtering enhances image quality by removing high spatial frequency noise.